The effects of stance configuration and target distance on reaching

Abstract

The aim of the present study was to investigate the relationship between the focal and postural components of a functional movement during the preparatory phase of a task. The contribution of the arms, trunk, and legs were varied by having subjects reach for two targets within and two beyond arm's length. In addition, the degree of postural stability was manipulated by varying the size of the base of support (BoS). Nine subjects reached and grasped a dowel placed at four locations while standing on a force plate with their feet in a parallel or step stance (right foot forward) under simple reaction-time (RT) conditions. Anticipatory postural adjustments (APAs) occurring prior to arm movement and RTs were analyzed. APAs varied depending on the demands of the task. For movements within arm's length, subjects selected different strategies to initiate the movement. However, for movements beyond arm's length, all subjects used the same strategy: the center of pressure (CoP) was shifted posteriorly, which resulted in the center of mass (CoM) moving towards the target. Target distance and BoS had no effect on the onset of APAs. In contrast, amplitude and duration of APAs increased linearly with target distance, and amplitude was always greater during the more posturally stable BoS configuration. Although wrist RT increased linearly with movement amplitude for both stance configurations, the rate of change was less under the more stable BoS. These results suggest that, during the performance of a functional task, dynamic changes that occur in the trunk and lower extremities prior to initiation of arm movement serve not only to stabilize the body, but are also used to initiate and assist whole-body reaching.

Reliability and Validity of the Hand Reach Star Excursion Balance Test

“…Hand reaches beyond arm's length from standing elicit a dual role of the trunk and lower extremities in both postural stability and joint movements in transferring the hand to the target, linking posture and movement coordination [9][10][11]. As reach distance increases, the trunk, upper and lower extremities work together as one functional unit to move the body toward the target [9] with a greater movement of center of the mass (COM) [9,11] and increased joint movements [12].…”

The Effect of the Base of Support on Anticipatory Postural Adjustment and Postural Stability

“…So, postural stability is increased So, postural stability is increased. 11,26 From the previous studies, we know that area size of the base is connected with postural stability. And then, we know that there were many previous studies of COP displacement characteristics or muscle onset time which reflects the APA characteristics of postural muscle.…”

Effects of Repetitive Reaching Movements on Performance and Postural Control

“…Subjects were asked to reach to a small target with the right arm as fast as possible after a brief beep sound. The beep signal was provided at a random interval of 2-5 s after subjects had attained an upright posture 14) . The target (diameter, 2 cm) was positioned at shoulder height to the front and center of the subjects' bodies.…”